Behçet's disease (BD) is a multisystem vasculitis that may involve vessels of all sizes. Acute coronary syndrome (ACS) due to secondary involvement of BD is rare and its management less clear. In this case, a 29-year-old man admitted to the emergency room with ongoing chest pain was interned to the coronary care unit with a diagnosis of ACS. The patient had been diagnosed 1 year before with BD and had been without regular follow-up, despite the suggested use of cholchium. An immediate coronary angiography revealed a fresh thrombus image in the proximal segment of the right coronary artery (RCA), an aneurysm of the left anterior descending artery (LAD) at proximal segment, and a hemodynamically significant lesion following the aneurysm. Intervention was ended because of normal flow (TIMI III) of distal RCA. An intravenous infusion of glycoprotein IIb/IIIa receptor inhibitor (tirofiban) was administered, and a control angiography showed dissolution of a thrombus in RCA, but enlarged aneurysm of LAD and a new aneurysm in RCA.